From my expeience, a miscellaneous category is a must. You will always get an occation where it will not fit into one of the pre-defined categories, for example, I got a help desk call when the building flooded, and the electricity went off. Not exactly an IT problem, but one that needed logging anyway.
It also depends on how you are going to use the category. Is it the reason the person called, or are you going to change it in order to reflect what the actual problem/solution was. E.g. Cannot open a page in internet explorer could be logged as Website, network, or software problem. It may then be apparent that the problem is a failed port on a switch at which point it becomes a network or hardware problem.
As for priorities, there should be nothing which can be logged above high, and most things should be logged at medium or low. Urgent or very high should be determined by the helpdesk operative, as the priority for resolution is dependant on the other work in the queue, which the end user will not be able to see. For example, a PC with a blue screen of death the end user will be an urgent problem, however, if someone goes and fixes that over sorting out the switch that has just failed, then they are no better off, as once the machine is fixed, they still cannot access network resources.
I would in an ideal world not allow end users to log above Medium themselves, and only be able to excelate it following discussion with a helpdesk operative.
Hope this helps.
Andy
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So often times it happens that we live our lives in chains
And we never even know we have the key
Ne auderis delere orbem rigidum meum
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